Resin laminates formed by laminating a polyamide-based resin layer and a fluorine-containing ethylenic polymer layer are expected as composite materials having fluororesin characteristics, such as heat resistance, oil and chemical resistance and low liquid agent permeability, as well as polyamide-based resin characteristics, such as high strength, high toughness, light weight, good processability and, in particular, flexibility.
However, the polyamide-based resin layer and the layer comprising the fluororesin such as a fluorine-containing ethylenic polymer are generally low in interlayer adhesiveness. Therefore, attempts have so far been made to increase the interlayer adhesion strength. Thus, for example, Japanese Kokai Publication Hei-05-8353 discloses a multilayer tube comprising an outer layer comprising a polyamide resin and an inner layer comprising a fluororesin. In the gazette cited above, it is proposed that, for securing a certain level of adhesion strength between the polyamide resin layer and the fluororesin layer, crosslinked structures are introduced among molecules in both layers by irradiation.
A technology has also been developed according to which the resin layer to be adhered to a polyamide-based resin is made of a blend with a fluororesin. Thus, for example, Japanese Kokai Publication Hei-07-53823 discloses a multilayer tube comprising an outer layer comprising a polyamide resin and an inner layer comprising a fluororesin, wherein a resin composition comprising both a specific polyamide resin and a fluorine-containing resin is laminated to the polyamide resin layer so that it may serve as an adhesive layer. When this method is used, however, the morphology of the adhesive layer changes according to the molding conditions due to the intrinsically poor compatibility between the constituent resins of the adhesive layer, namely the polyamide resin and fluorine-containing resin, and the morphology change influences on the cohesive force of the adhesive layer itself and on the adhesion strength thereof with the other layers. Accordingly, such problems arise as a tendency toward variation in adhesion strength according to environmental factors, such as molding conditions and temperature conditions during use, and difficulty in securing a constant quality level. In addition, this is not a technology to increase the adhesiveness of the fluororesin itself but one merely utilizing the adhesiveness of the polymer blend. The use of such polymer blend in lieu of the fluororesin results in an impairment in those excellent characteristics of the fluororesin.
To solve this problem, attempts have been made to improve fluororesin species themselves, and various fluororesin materials have been proposed. For example, the WO 99/45044 pamphlet discloses a laminate which comprises a fluorine-containing polymer having carbonate groups and/or carbonyl halide groups as a fluororesin to be laminated with a polyamide resin.
However, any of these technologies does not disclose an improvement in polyamide-based resins themselves. Therefore, from a novel technological viewpoint, a technology is demanded of further improving the interlayer adhesion strength between a polyamide-based resin and a fluororesin.
Thus, there are demands for molded articles, such as tubes, hoses, bottles and tanks, which are imparted with good mechanical properties and high resistance to environmental factors such as heat and various chemical substances by providing a polyamide-based resin as an outer layer and, further, demands for molded articles which can realize high levels of oil and chemical resistance and low liquid agent permeability in such moldings as tubes, hoses, bottles and tanks by providing a fluorine-containing resin as an innermost layer, in particular demands for such good multilayer molded articles which can be molded by co-extrusion molding and be markedly and stably improved in interlayer adhesion strength.